1. Field of the Invention
The present invention relates to film coatings having improved pearlescent qualities. The invention also relates to pharmaceutical substrates having such film coatings and methods of preparing the same.
2. Description of the Prior Art
Over the years, considerable effort has been expended to increase the visual appeal of tablets and capsules. Many pharmaceutical manufacturers attempt to establish brand identity for their newly-approved products by altering the shapes, colors, etc. of the dosage forms. It has been proposed that consumers develop greater brand loyalty for distinctively appearing products as compared to those containing the same active ingredient in an unremarkable appearance, i.e. a white compressed tablet.
It has also been proposed that imparting a pearlescent appearance to tablets, etc would provide a means of further differentiating new products, even from those having a bright or highly polished finish coat. One such coating currently marketed to provide a pearlescent or nacreous quality to various products is sold under the trade name Candurin® by Merck KGaA. The pearlescent pigments are titanium oxide and/or iron oxide pigments supported on a base of lamellar substrate comprising mica or flakes of Al2O3, SiO2 or TiO2.
PCT patent application having publication number WO 00/03609 discloses coated articles prepared using Candurin pearlescent pigments. Among the articles coated are sugar products (e.g. caramel), cake decorations, chewing gum, chocolate, ice cream, cereals, snack products, nonpareils, gelatin products, candy, licorice, icing, cream compositions, tablets and capsules. The coating materials which can be included with the pearlescent pigments are sugars, shellacs (both aqueous and ethanolic), polymethacrylates and “cellulose types” including specifically hydroxypropylmethylcellulose (HPMC) and Sepifilm® LP (HPMC, microcrystalline cellulose (MCC) and stearic acid). Although the publication discloses addition of conventional colorants to the pearlescent compositions, there is no mention of how to obtain a high gloss finish on pharmaceutical dosage forms, either by formula or process modifications/optimizations.
Additionally, U.S. Pat. No. 6,627,212 discloses of using special effects pigments in ingestible drugs. Examples include mixtures of platy titanium dioxide pigments, titanium dioxide and/or iron oxide coated on inorganic platy substrates and combinations thereof, with ingredients, such as carnauba wax, isopropyl alcohol, and gelatins, to impart an optical effect to the coated and/or imbedded articles. Once again, however, there is no mention of how to obtain a high gloss finish on pharmaceutical dosage forms.
Other attempts have been made at improving the appearance of tablets. For example, U.S. Pat. No. 4,576,646 discloses providing tablets with a coating having a satin appearance. In addition, commonly assigned U.S. Pat. No. 6,420,473 discloses acrylic enteric coating compositions which can contain, inter alia a pearlescent pigment based on mica and/or titanium dioxide. Coatings produced from these formulations, however, have relatively low gloss. Enteric coating compositions are highly specialized to assist in delivering a pharmaceutical active to the intestines and, therefore, not generally applicable to immediate release dosage forms. Due to the physical characteristics of typical enteric coating systems, the coating finish is generally of low gloss.
In spite of the foregoing, further improvements have been sought. For example, it has been found that it would be desirable to provide a higher gloss finish for tablets and other substrates having pearlescent coatings. The present invention addresses this and other needs.